The present invention relates generally to a low altitude or ground proximity warning system, particularly for fighter aircraft.
Ground proximity warning systems that warn of a hazardous condition are known. Examples of such systems are disclosed in several U.S. patents to Bateman, including U.S. Pat. Nos. 3,934,221 and 3,946,358, on a Ground Proximity Warning System (GPWS) assigned to Sunstrand Data Control, Inc. These systems monitor the radio altitude and the radio altitude closure rate, and generate a warning if the rate of closure rate is excessive for the altitude at which the aircraft is flying. While these systems do provide a way to warn the pilot of a hazardous condition resulting from an excessive closure rate with terrain, these systems are designed for use in transport aircraft, and not for use in high performance tactical aircraft such as fighter or attack aircraft whose flight and operational characteristics are substantially different than those of transport aircraft. Consequently, the systems designed for transport aircraft can provide false warnings during certain normal operational conditions of a tactical aircraft, and provide no warning or an inadequate warning during other flight conditions.
Canadian Pat. No. 1,033,828 to Cheng et al and assigned to Litton Industries on a "Digital Ground Proximity System for Reducing False Warnings" discloses a system which stores a representation of a warning envelope which is a function of a warning parameter vs. radar height. A device iteratively makes a determination to provide a warning signal if the aircraft flight conditions place it within the warning envelope.
Other U.S. patents of interest include U.S. Pat. Nos. 3,530,465 to Treffeisen et al, 4,058,710 to Altmann, 4,121,287 to Leal et al.
The operational and flight characteristics of a high performance aircraft such as a fighter or an attack aircraft are considerably different than those of a transport aircraft. For example, it is quite common for a high performance tactical aircraft such as a fighter or attack aircraft to fly at low level over various terrain including rising and falling terrain. Much of the low altitude flying is done at high speed and steep attitudes, and consequently, it is possible for the pilot inadvertently to fly the aircraft into terrain, particularly if the aircraft is being flown over gradually rising terrain. Consequently, it is desirable to provide the pilot with a warning of an impending flight into terrain with sufficient time to permit him to take corrective action. However, systems designed for transport aircraft generally would not provide suitable warnings, since such aircraft typically do not fly at the relatively low cruise altitude flown by tactical aircraft. As a result, systems designed for transport aircraft would tend to give inadequate and false warnings, and such warnings would be a nuisance to the pilot.
Patterson et al U.S. Pat. No. 4,639,730, also assigned to Sunstrand, is a warning system for tactical aircraft, that monitors the closure rate of the aircraft when the weapons are not armed, the aircraft is flying between 100 and 1,800 feet, and the airspeed exceeds 200 knots, and provides a warning to the pilot if the radio altimeter rate exceeds a predetermined safe limit for the radio altitude at which the aircraft is flying.
Controlled Flight Into Terrain (CFIT) constitutes a large category of mishaps. A CFIT occurs when the pilot's attention is diverted, or when the pilot becomes disoriented. CFIT warning systems have been mandatory on commerical aircraft since 1976. The Air Force has installed systems on some transport aircraft. However, considering the mission scenarios and performance capabilities of fighter/attack aircraft, these systems have not proved suitable to tactical situations. There is a need to provide improved warning systems for tactical aircraft.
Low altitude or ground proximity warning systems have proven to be unsatisfactory to the user pilots primarily due to excessive nuisance warnings being generated. In addition, warning protection was not adequately provided for all mission tasks which required protection. The problems of protecting fighter aircraft which fly hard maneuvers close to the ground while trying to attack or escape is immensely more difficult than providing warning protection to high flying low maneuverability aircraft which have no other requirement than to fly smoothly from point A to B. Previous attempts to adapt commercial warning systems to fighter aircraft failed. Further, due to the cumbersome design approach which required large amounts of information stored in memory, the similar warning systems required dedicated computers. In addition to this having been demonstrated to be significantly more expensive than inbedding warning system logic into on-board computers (which is generally not possible with large memory progrmas) there is the physical size and cooling requirements of an additional computer which, for the F-16 for example, was impossible to accommodate. Physical space requirements on a large aircraft are not generally limiting.